The present invention relates to telephone equipment, particularly to an apparatus and method for automatically determining the status of a telephone call which has been placed by the apparatus.
Apparatus for automatically placing telephone calls to deliver prerecorded messages have, in the past, suffered from a disadvantage of not being able to recognize the signals that indicate call progress. Such automatic callers can be programmmed or arranged to deliver a recorded message to people on a list, given their phone numbers. The automatic caller could dial the respective telephone number for an individual, but would not know whether the call was ringing or answered, or whether the line was busy, out of service, etc.
One possibility is to use a phone handset hangup click detector which responds to the noise or signal which is generated when a telephone party hangs up the telephone. The same noise occurs when a called party answers the telephone. Circuits have been devised for detecting such noise, and a hang-up detector cooperating with a timer is one combination which can be used to learn some information about call progress. Basically, the timer would be set for some arbitrary time, such as 30 seconds. If there were no answer click, as detected by the hang-up detector, within the 30 second period, then the automatic telephone caller would assume that the call could not be completed and release the telephone line. The primary disadvantage of such a system is that it does not know whether the called telephone number resulted in a ringing signal, a busy signal, or a different signal. In other words, it does not identify call progress tones.
Accordingly, prior to the present invention there has been a need for a call progress tone detection circuit which would be capable of ascertaining the progress of each phone call which had been placed by the automated equipment. It is therefore one object of the present invention to provide a method and apparatus for achieving this purpose.
One complication in achieving this goal is the lack of an industry standard on the precise characteristics of the tones which connote various states. There is variance in call progress tones among American Telephone and telegraph telephones (the "Bell System"), the General Telephone and Equipment telephones, and other, independent telephone companies. Because an automatic caller places calls throughout the United States, a call progress tone detection circuit which is designed for use with such an automatic caller must be capable of recognizing any call progress tones, regardless of the telephone system which generates those tones. It is therefore a further object of the present invention to provide such a call progress tone detection circuit.
Still another object of the present invention is to provide a call progress tone detection circuit which is not unduly complicated, uses little space on a printed circuit board, and uses little hardware. In other words, a further object of the present invention is to provide a call progress tone detection circuit which is accurate, inexpensive, and compact.